Programmable toner concentration control

ABSTRACT

A toner concentration control is provided including a programmable toner pickup with surface areas at selected electrical potentials to simulate background and image areas of a predetermined image pattern. By changing the potential applied to each of the pickup surface areas, the simulated conditions and copy density may be adjusted. The concentration of the toner deposited on the pickup is compared with that of an ideally developed image and additional toner is controllably dispensed to maintain the selected copy density.

United States Patent Griesmer Oct. 14, 1975 [54] PROGRAM [ABLE TONER 3,791,744 2/1974 Erny et a]. 118/637 X CONCENTRATION CONTROL 3,801,196 4/1974 Knapp 355/3 3,818,864 6/1974 Bickmore... 118/637 [75] Inventor: Jerome John Griesmer, Mentor,

Ohlo Primary ExaminerMervin Stein 73 Assignee: Addressograph Multigraph Assistant EXami'1erDOuglaS Salser Corporation, Cleveland, Ohio Attorney, Agent, or Firm-Harry M. Fleck, Jr.

1 1 pp N01 421,226 A toner concentration control is provided including a programmable toner pickup with surface areas at se- 52 us. c1. 118/7- 11s/11- 118/637 acted electrical Potentials Simulate background 51 Int. Cl. BO SC 11/00 and image areas a predetermined image BY 52 Field 01 Search 118/7, 9, 10, 11, 637; Changing the POtemial applied to each of the Pickup 1 17/175 surface areas, the simulated conditions and copy density may be adjusted. The concentration of the toner [56] References cued deposited on the pickup is compared with that of an ideally developed image and additional toner is con- UNITED STATES PATENTS trollably dispensed to maintain the se1ected copy den- 3,580,673 5/1971 Yang 355/15 i $682,132 8/1972 Kamola 118/7 3,756,192 9/1973 Locklar et al. 118/7 22 Claims, 6 Drawing Flgures US. Patent Oct. 14, 1975 PEAK 0E7:

Z 06 AMP PROGRAMMABLE TONER CONCENTRATION CONTROL BACKGROUND OF THE INVENTION This invention relates to electrostatic copying and, more particularly, to an improvement in automatically controlling the concentration of the toner component in a developer mix applied to elcctrostatically imaged copies.

Electrostatic copying, as is well known in the art, comprises the steps of charging a photoconductive surface, exposing the charged photoconductive surface to a pattern of light and shadow representative of the graphic information to be copied, developing the resultant charge pattern which corresponds to the graphic information by applying a charge attractable toner powder to the photoconductors surface; and causing the toner powder to be fixed to the photoconductive surface in the areas where the image is desired.

It is conventional in this art to formulate the developer mix so that the appropriate triboelectric forces are generated, imparting the necessary triboelectric charges to the particulate matter comprising the mix. Typically, developer mixes are made up of toner particles and larger carrier particles and the materials selected are such that the rubbing contact between the dissimilar particles will generate the necessary and appropriate triboelectric charge. Under the influence of the triboelectric forces the toner particles cling to the carrier particles until separated therefrom by a greater attractive force.

In order to render the charge pattern visible, the developer mix can be flowed, brushed or cascaded over the differentially charged surface which provides the attractive force to separate the toner from the carrier and to attract the toner to the areas which are to be rendered visible.

The foregoing brief description of the developer mix technique for developing electrostatic images will suffice for the purpose of providing the necessary background of this invention. The details of toner composition, copier materials, and the makeup and operation of developer mixes generally are all well known and need not be dealt with in this presentation.

One of the significant problems in this art has been to consistently produce high quality reproductions using the known developer mix technology. Many variables are present which can affect the qualtiy of the reproduction, such as the concentration of toner in relation to the carrier particles. The concentration is everchanging due to the depletion of toner from the mix during the reproduction cycle. Too little toner or too much toner can result in images of improper density which are light in color or dark in color. In addition, poor contrast in the copy may result from the attraction of powder in the non-image areas. It has been found that there is a correlation between the triboelectric forces generated and concentration of the mix components. There is a balance that must be maintained such that the triboelectric force is optimized as a function of the concentration of toner in the mix and also as a function of the electrical field emanating from the charge pattern.

It is important to recognize that underlying the quality of the reproduction is the charge level on the surface to be developed. Since the toners are electroscopic materials, they respond to differences in potentials in a given charge pattern. The image and nonimage areas correspond to the pattern of light and shadow generated from the graphic subject matter to be reproduced and compete with each other to attract the toner particles. Small differences between image and non-image areas will produce less attraction to the image areas, while greater differences provide greater attraction of the electroscopic materials toward the image areas. Hence, the nature of the charge pattern on the photoconductive materials is important. The amount of toner attracted to the latent image is dependent upon the degree of darkness at any particular point of the image and the ratio of that darkness to the lightness throughout the entire image. More toner will be deposited in an area where the image is extremely dark than in an equal area which is only moderately dark.

A number of control systems have been proposed to automatically sense and regulate the concentration of toner powder at a developing station. One such device utilizing an electrical resistance measurement to con trol toner concentration is further described in U.S. Pat. No. 3,527,651. Another such device using an induetivc probe is described in U.S. Pat. No. 3,707,134. Still other devices use optical sensing of light reflected from a probe or capacitive change ofa probe in the developer mix to control the concentration. However, for the most part these devices met with only marginal success and were ineffective in maintaining acceptable copy density. This was particularly true when the mix aged considerably. Ageing often causes changes in the characteristics of the mix, such that the signals provided by these devices are not truly representative of the toner concentration.

U.S. Pat. No. 3,348,521 discloses a device which uses a photoconductive surface of extended length on a drum with a permanent electrostatic image thereon located outside the area necessary to develop copies, but still within the operating zone of the developing apparatus. The photoconductive surface is periodically developed and cleaned along with the image area and a photosensor is provided which detects the optical density of the deposited toner. This arrangement generally provides only marginally satisfactory results and has a number of deficiencies. First, the photoconductive surface is provided with a permanent electrostatic image which is not readily changeable to compensate for different image and background conditions. Secondly, each time the photoconductive surface is cleaned, toner is removed from the system, thereby increasing the amount of toner which has to be added to the mix to maintain a satisfactory concentration. Thus, this type of system cannot be adjusted to simulate different image pattern conditions and its operation continually depleats toner from the developer mix. Thirdly, the system is not capable of adjusting for changed signal strength due to contaminants on the image surface.

SUMMARY OF THE INVENTION It is a primary object of the present invention to pro-v vide a novel toner concentration sensing system including a sensor member which is programmed to simulate selected image and background conditions.

Another object of the present invention is to provide a versatile toner concentration sensing system including a sensing member having separate surface areas with different electrical potentials applied thereto, corresponding to image and background areas, respectively, to accurately simulate a latent image pattern.

It is another object of the present invention to provide a unique toner concentration sensing system including circuit means for providing readily adjustable electrical potentials to a sensing member to simulate selected background and image conditions, whereby a toner concentration reference level is provided which is a function of the selected image pattern conditions.

Still a further object of the present invention is to provide a toner concentration sensing system including a sensing member which is periodically developed and cleaned independently of the latent image pattern and without depleating the toner from the developer mix.

It is still another object of the present invention to provide a versatile toner concentration sensing system including a sensing member which is in operative engagement with the developer toner applicator, whereby the sensor member is developed in the same manner as the latent image pattern on the photoconductor, but is subsequently cleaned independently of the photoconductor in a manner which returns the toner directly to the mix.

Yet a further object of the present invention is to provide a unique toner concentration sensing system which automatically adjusts for changes in signal strength due to contaminants on the sensing member or changes in reflectivity thereof over a period of time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic illustration of the sensor of the present invention utilized with a magnetic brush type developer.

FIG. 2 is a partial plan view of the sensor member in operative engagement with a magnetic brush and mounted adjacent to a photosensor unit.

FIG. 3 is a diagrammatic illustration and flow diagram of the circuitry associated with the present invention.

FIG. 4 is a graphical illustration of the relationship of the electrical potential applied to the sensing Wheel they vary with time.

FIG. 5a is a developed view of the sensing wheel showing the toned and cleaned areas defined by applying potential in a preferred arrangement as a function of time.

FIG. 5b is a developed view of the sensing wheel as showing a toned and cleaned area defined by applying potential in a second manner as a function of time.

DETAILED DESCRIPTION Although the figures show the device of the present invention being used with a magnetic brush developer, the reader should appreciate the fact that the invention can be used to advantage with any of the developing techniques present in the prior art.

In FIG. 1 a recording member 10, such as a photoconductor in the form ofa cylinder, is shown in contact with developer mix 12 carried by a magnetic brush 14. The magnetic brush 14 applies toner from developer mix 12 onto the charged latent image pattern on the recording member in a well-known manner. U.S. Pat. Nos. 3,003,462 and 3,145,122 describe more fully the operation of the magnetic brush 14. During rotation, brush 14 is brought into engagement with mix stored in a trough or container 13, whereby the developer mix is replenished on each revolution. Preferably, both the LII recording member 10 and the magnetic brush 14 are of generally cylindrical configuration. A sensing wheel, or toner pickup, 18 is provided which makes operative contact with the mix carried by magnetic brush 14, but is spaced from the recording member 10. An optical read head 20 is positioned to detect changes in concentration of toner deposited on the sensing wheel 18.

Before describing the sensing wheel 18 and optical read head 20 in detail, a description of the operation of the device would be helpful. Basically, an electrostatic image of the copy to be made is produced on the recording member 10 according to techniuqes known in the prior art. Developer mix, as previously described, is picked up by the magnetic brush 14 by an appropriate method well-known in the art. As the recording member 10 rotates about its axis 11, it makes contact with mix carried by brush 14, such that toner powder is attracted to the image areas on the recording member 10. In this manner, the image of the copy to be made is completely developed by the toner transferred from magnetic brush 14.

Transfer of toner is caused by the attraction of charged toner particles to imaged or non-imaged areas of a photosensitive surface. To effect this transfer properIy, first the photosensitive surface must be charged uniformly and then selectively discharged in the desired non-image areas. Next, the toner developer powder which consists of carrier particles, i.e., iron fillings or glass beads, and toner particles is applied to the photoconductive surface. It will be appreciated that while the invention is herein described as sensing the concentration of toner in a powder mix, it might be utilized with liquid developer mixes as well.

The actual polarity of the charges presented by the toner developer powder and the photosensitive surface is not extremely important. However, the polarity of the toner powder charge must be opposite to the polarity of the charged surface in the area where toner is desired to be deposited. Along these lines, positive and reversal images may be obtained depending upon the polarities chosen for the toner developer and the image.

An example of the basic toner transfer process as applied to both positive and reversal images, is disclosed by U.S.' Pat. No. 2,874,063. Very briefly, in the process carrier particles and toner particles are triboeleetrically charged to cause attraction towards each other. Thus, positively charged carrier particles will attract negatively charged toner particles. Likewise, the photosensitive surface is charged by a light exposure pattern which causes effectively, heavily positive charged image areas and background areas being of light positive charge or neutral. The actual charges on the photosensitive surface may be represented by a series of voltage gradients or changes in potential over the surface of the photoconductor. This change in voltage potential, A is measured with respect to imaged areas as compared to nonimaged areas. With most magnetic brush developing systems, transfer of the toner particles is also influenced by the potential of the brush core relative to the image area potentials.

Toner response is a term which may be used to express the relative quantity of toner particles which actually become attracted to the charged image. More particularly, this may be expressed in terms of the mass of toner per unit area. If the image and potential thereof are held constant, the amount of toner attracted to the image area depends upon the concentration of toner in the developer mix. The system of the present invention detects the amountof toner deposited on an image area at a selected potential and causes toner to be added to the mix when the detected toner concentration reaches a predetermined minimum level. Thus, the system is responsive to the mass of toner deposited per unit area.

As the recording member and magnetic brush l4 rotate, the sensing wheel 18 will be subjected to the developer mix on the surface of the magnetic brush 14. If a charge pattern, analogous to that of an image, is present on the sensing wheel I8, toner powder will be attracted to the sensing wheel. However, when no charge pattern is present on the sensing wheel 18, no toner powder will be attracted.

As discussed above, by providing potential differences or voltage gradients, a charge pattern analogous to a particular image may be synthesized. In this manner, voltages are applied to the sensing wheel 18 to establish potential differences representative of a selected image pattern. These potential differences result in charge patterns which attract toner particles and develop selected image depending upon the polarity of the charge patterns and the toner. The selected potential established on the sensing wheel 18 represent variations of possible image densities. That is, the sensing wheel l8 is capable of simulating varying degrees of image lightness or darkness in addition to a range of background conditions. Potential differences applied to the sensing wheel 18 are arranged to span the range of image densities to be expected.

When considering the potential differences to be ap plied to the sensing wheel 18, the subject of positive and reversal image development should be discussed. In this regard. the development of the image simulated on the sensing wheel I8 does not depend upon either a positive or reversal image. However, since the read head 20 in this embodiment performs an optical reading function, the systems should be arranged so that proper control of the toner particles is effective regardless of whether positive or reversal images are being used. Additional toner should he added to the mix when the concentration of toner on the developed portion of the wheel as sensed by the read head 20 falls below a predetermined minimum.

If the simulated image on the sensing wheel, or toner pickup, 18 were to be established once and continually developed, toner particles would have an accumulative effect on the optical sensing. Therefore, in the case of the present invention, the simulated image (potential) is removed and re-established for each development. Regardless of the charge potentials established on the sensing wheel surfaces. the present invention periodically cycles the establishment and cancellation of the change pattern with rotation of the sensing wheel. This cycling of the charge pattern is effected, for example, by an electromechanical cam structure causing the simulated image to be altered, say three times for each revolution of the sensing wheel 18. In this way, the magnetic brush 14 appears to be developing a completely new image for each revolution of the sensing wheel 18. Also, the image potentials actually programed onto the sensing wheel 18 may be selectively changed in magnitude to provide a new toner concentration level. In ad dition, the circuitry looks at the sensing wheel when it is clean as well as when toner is deposited. In this way,

the circuit corrects for slight changes in the strength of the signal from the optical read head due to contaminants or changes in the reflectivity of the wheel surfaces.

Referring now, more particularly, to FIG. 2 of the drawings, the preferred construction of the sensing wheel associated with the present invention may be seen in more detail. Sensing wheel 18 is driven by a motor, not illustrated, in a direction indicated by the arrow in FIG. 1. The sensing wheel 18 is relatively short in axial length and, as such, makes contact with only a small axial portion of magnetic brush 14. The sensing wheel 18 is constructed of a number of cylindrical discs 22, 23 and 24 of a material electrically conductive in nature. Insulating discs 26 are positioned at the common abutments of the conductive discs 22, 23 and 24. The two outer electrically conductive discs 22 and 24 are electrically connected to a brush and slip ring 25 by internal wires, not illustrated. Similarly, inside disc 23 is connected to a second brush and slip ring indicated by the numeral 27. In this manner, one electrical potential is connected to the outside two conductive discs 22 and 24 and another electrical potential is connected to the inside conductive disc 23, causing a potential difference to exist across sensing wheel 18.

Preferably, the sensing wheel is coated with semiconductor material in order to prevent direct shorting at the magnetic brush interface. Also, this effectively divides each of the discs into separate surface areas which substantially retains the charge impressed thereon while in contact with the magnetic brush. Thus, it is possible for a portion of sensor disc to have toner while another portion does not, to provide a series of toned and untoned areas around the disc which are seen by optical sensor 20, as hereinafter explained.

As mentioned above, this electrical potential difference is used to simulate a charged image. In the case of the actual image on the recording member 10, there is a potential difference between the image and background, causing toner to be attracted to the image rather than background. Likewise, the potential difference established on the sensing wheel 18 simulates the conditions of the image and background area. The values of the electrical potentials applied to the sensing wheel 18 correspond to specific image or background potentials. The values of the voltages applied to the sensing wheel are arranged to cause the simulated image to appear initially on the center conductive disc 23. At the same time, the simulated background appears on the outside conductive discs 22 and 24.

Optical read head 20 is positioned to read only the center conductive disc 23 to perform its intended function. A light source 30 is provided which directs light onto the surface area of center disc 23. Preferably, a light dispersing member 32 is included in the light path from light source 30, to assure that no light reflected from the walls of the path of light on the way to the sensing wheel 18 affects the sensing. The light which is reflected from the surface of center disc 23, which may or may not have toner powder on it, is directed to a conventional photoresponsive device 36 through a dispersing member 34. The purpose of the dispersing member 34 is to assure that the optical density is not affected by reflections from parts of the read head 20 itself. Any scheme which does not allow light to be reflected from the walls of the passage through which the light passes to and from the sensing wheel 18 serves the purpose intended. In the case of this particular embodiment. the scheme used involves producing ordinary helical thread along the walls of the passage. The effect is to not allow any light impinging upon the inside surfaces of the passage to re-cnter the directed beam of light. In addition, surfaces of the read head are dark in color in order that toner deposits upon the head not affect the reflectivity of light. It is also desirable to provide air currents in the vicinity of the read head which prevent toner powder from being deposited on read head 20.

Once an image has been simulated on the sensing wheel 18, the image is developed by toner deposited from the magnetic brush 14 as the sensing wheel rotates with the conductive disc 22, 23 and 24 surfaces in contact with the magnetic brush 14. The read head 20 then. detects the optical density of the simulated image on conductive disc 23 by sensing the intensity of light reflected from the surface area of conductive disc 23. The larger the concentration of toner on this surface area, the lesser is the reflected light intensity. In this regard, it has been found that the specular reflection of light, measured in density units, off of the deposited toner is inversely proportional to the mass of toner per unit are. This relationship may be expressed by the equation:

n-I) D. U. log HIT where I is the photosensor current without toner, and l,-,,, is the photosensor current with toner deposited on the sensor wheel. This relationship is reasonably accurate for detection purposes over a range of two density units. It will be appreciated that this relationship takes into consideration the specular reflection of the surface area without toner. Since the system periodically removes toner from the surface area of the sensor disc, the specular reflection is periodically monitored such that changes in the reflective characteristics of the surface are compensated for in each and every detection. This is most important as contaminants, other than toner, are likely to accumulate on the wheel over a period of time. In addition, the reflective nature of the wheel surfaces may become more diffuse over a period of time due to wear caused by rubbing of the iron carriers.

FIG. 3 is a block diagram of a typical electrical circuit used to detect and compare the developed simulated image. The light responsive device in this case is a photo transistor 36 which is connected to a conventional logarithmic amplifier 38. The logarithmic amplifier is used since the density unit change is directly proportional to the log of the ratio, current untoned to current toned as set forth in the above equation. The output of this logarithmic amplifier 38 is then connected directly to an appropriate peak-to-peak detector 40, as are well known to those skilled in the electrical arts. The function of the peak-to-peak detector 40 is to provide an output signal representative of the total change in optical density between the toned and untoned sensed on disc 23. The output of the peak-to-peak detector 40 is fed to a conventional comparator 42, which compares the total change in optical density with the optical density of an ideal image. Finally, the output signal from the comparator 42 is connected to an appropriate control circuit 44 which activates a conventional dispenser when required. Such toner dispensers are well known and it is not intended that such constitute a part of the present invention.

In actual practice, the image is programed onto the sensing wheel 18 by selectively adjusting a potentiometer associated with the power supply and program control 54. This adjustment determines to a greater or lesser extent the attraction of toner to the sensing wheel and the amount which will be deposited per unit area if the toner concentration in the mix is ample. When the toner concentration falls below a minimum level, the amount of toner picked up by the wheel will likewise diminish to provide an appropriate signal from comparator 22 which causes toner to be added to the mix. It will also be appreciated that since the potentials correspond to image and background areas, the sensing wheel accurately simulates the conditions of developing an actual copy.

In order to provide continual sampling or monitoring of the toner concentration in the mix, the potential on center disc 23 is periodically reversed in polarity relative to the magnetic brush core. This reverses the direction of the net electrostatic field at the interface between the brush and the sensing wheel, whereby toner powder previously deposited on the sensing wheel is returned to the brush. In the preferred embodiment, this occurs three times for each revolution of the sensing wheel. Of course, a greater or lesser number of revolutions may be utilized, if desirable, to do so.

Referring now, more particularly, to FIG. 4, a graph of the potential applied to the center disc 23 as a function of time and wheel position is illustrated in solid line. The potential of the magnetic brush core is indicated by V,. and is maintained constant, as indicated by line 48. V;,,, represents the image area potential, while V,,,, corresponds to the background potential. As mentioned above, the potential applied to center disc 23 is reversed three times per revolution of the sensing wheel. With V,-,,, impressed on center disc 23, as indicated at 50, toner is attracted from magnetic brush 14. After the sensing wheel has rotated one-third of a revolution, V is applied to sensor disc 23, as indicated at 52. This causes the positive toner particles to return to the magnetic brush in the area of the interface. This potential remains on the center disc for the second third of the revolution, after which V is again applied to cause toner to be attracted to the wheel in the area of the interface with magnetic brush 14. The time during which this potential is applied is indicated by the numeral 54 and continues until one wheel revolution has been completed as indicated at 7rD.

It is important to note that while the potential on center disc 23 is reversed, the transfer of toner from the wheel does not occur, except in the area of contact with magnetic brush 14. Thus, some areas of the sensor disc will remain toned while the other is cleaned. This is illustrated by FIG. 5a, with areas 23a and 23c being toned and area 2312 being relatively clean. Thus, as the sensing wheel is rotated, optical read head 20 sequentially detects toned and untoned areas to provide the desired system response by way of log amplifier 38 and peak-to-peak detector 40. It will be appreciated that since an odd number of program cycles is provided for each revolution of the sensing wheel, previously toned area will be clean and vice versa each and every revolution.

It is also important to note that in the event contaminates should build up on the wheel, or if the reflectivity changes, which is sensed each time the sensing head looks at a clean areav This provides a new reference level via the peak-to-peak detector 40. If for some reason all of the toner is not removed during a cleaning cycle the system will compensate for such since the sig nal from the read head will be diminished due to the toner particles remaining on the wheel.

It will be appreciated that while the potential of the center disc is changed periodically, outer discs 22 and 24 are maintained at a constant potential corresponding to the image background. Typically, this potential is equal to the cleaning potential V,,, which is applied to the center disc. This is the arrangement illustrated by FIG. a.

If magnetic brush 14 is made of an insulating material, the center disc may be toned and cleaned more effectively if the potential applied to outer discs 22 and 24 are also changed as the potential on center disc 23 is cycled. Such an arrangement is illustrated by FIG. 5b and provides alternate toning and cleaning of the outer discs out of phase with the cycling of center disc 23. It has been found that this aids migration of the toner particles away from the center disc during the cleaning operation. Preferably, a V, potential is applied to the outer discs at the same time the cleaning potential (in this case V,,,,.) is applied to center disc 23. This results in toned areas of the outer discs, as indicated by 22!) and 2412, while areas 22a, 220, 24a and 240 remain clean. It should be noted that if the magnetic brush has sufficient response, the outer electrodes, 22 and 24, may not be required and only electrode 23 would be used.

Referring again to FIG. 4, it will be observed that the voltages indicated by dash line at 56, 58 and 60 correspond to the potentials applied to the outer discs as a function of time. In effect, with this arrangement, control 46 reverses the V,,,,- and V,-,,, potentials applied to the center and outer discs. It should be noted, of course, that it is not intended that the present invention be limited to cycling of the sensing wheel three times per revolution. Any odd number of program cycles may be utilized, if desired. The number of cycles per revolution, will depend to a large extent to the ability to deposit and remove toner to and from the sensing wheel and to the ability of the toner dispenser and related circuitry to respond to the various output signals. Multiple pass toning of the sensing wheel may also be desirable under some conditions, afterwhich a cleaning cycle would be implemented.

From the foregoing description, it will be appreciated that the present invention provide a versatile toner concentration control including a sensing member which is programmable to simulate an actual latent image pattern. By adjusting the electrical potential applied to the sensing member, the background and image conditions may be selected. Furthermore, the sensing system automatically ajusts for changes in signal strength due to contaminants on the sensing member or changes in reflectivity over a period of time.

In the above described system which utilizes a magnetic brush type developer for handling positive toner particles, the background voltage V,,,,. is in the range of 25-50 volts above the brush core potential V, The image potential V,-,,, is approximately 150 volts below the brush core voltage. Of course, it is not intended that the present invention be limited to the potential as such may be very dependent upon the paramaters of the overall system. Furthermore, it is not intended that the invention be limited to the specific circuitry illustrated in FIG. 3, or to the specifically described sensing head illustrated in FIG. 2. Various modifications of the circuitry may be made as will be obvious to those skilled in the art. Also, other types of sensing heads may be found to be appropriate for providing input signals to the system of the present invention.

While particular embodiments of the invention have been shown and described, it should be understood that the invention is not limited thereto, since many modifications may be made. It is therefore contemplated to cover by the present application any and all such modifications as fall within the true spirit and scope of the appended claims.

What is claimed is:

1. For use with an electrophotographic reproduction apparatus having a developer unit for depositing toner onto a latent image pattern from a developer mix con taining toner particles and carrier particles, a system for sensing the effective concentration of toner in the mix, said system' comprising:

toner pickup means for attracting the toner paticles from the developer mix handled by the developer unit and including a rotatably mounted pickup member separate from the latent image pattern and divided into at least first and second surface areas substantially insulated from each other,

means for rotating said pickup member,

program circuit means for applying a first electrical potential to said first area and a second electrical potential different than said first electrical potential to said second area, said first electric potential being of a polarity to attract the toner particles to said first area and corresponding to the imaged areas of the image pattern to be developed, said second electric potential corresponding to the background areas of the image pattern to be developed,

a source of light, and

means for sensing the light reflected from said first area to provide a signal representative of the light intensity.

2. The system set forth in claim 1 wherein said program circuit means applies said first potential periodically to said first area.

3. The system set forth in claim 2 wherein said program circuit means alternately applies a cleaning potential to said first area, whereby the deposited toner particles are periodically removed.

4. The system set forth in claim 3 wherein said cleaning potential is equal to said second potential.

5. The system set forth in claim 4 wherein said program circuit means alternately applies said first and second potentials to said second area.

6. The system set forth in claim 5 wherein said first and second areas are adjacent to each other to simulate the conditions of an image area and adjacent background area.

7. For use with an electrophotographic reproduction apparatus having a developer unit for depositing toner onto a latent image pattern from a developer mix containing toner particles and carrier particles, a system for sensing the effective concentration of toner in the mix, said system comprising:

member includes a third surface area electrically insulated from and axially adjacent to said first surface area, said first surface area being disposed intermediate said second and third surface areas, said program circuit means applying said second electrical potential corresponding to the background of the image pattern to said third toning area.

gram circuit means alternately applies said first and second potentials to said second area and to said third area.

tion apparatus having a developer unit for depositing toner onto a latent image pattern from a developer mix containing toner particles and carrier particles, a system for sensing the effective concentration of toner in the mix, said system comprising:

toner pickup means for attracting the toner particles from the developer mix handled by the developer unit and including a pickup member separate from the latent image pattern and divided into at least first and second surface areas substantially insu- 5 lated from each other,

program circuit means for applying a first electrical potential to said first area and a second electrical potential different than said first electrical potential to said second area, said first electric potential being of a polarity to attract the toner particles to said first area and corresponding to the imaged areas of the image pattern to be developed, said second electric potential corresponding to the background areas of the image pattern to be devell5 oped,

a source of light, and

means for sensing the light reflected from said area to provide a signal representative of the light intensity,

said pickup member comprising a rotatably mounted member associated with the developer unit, said first and second areas being axially disposed of each other.

8. The system set forth in claim 7 wherein said first and second areas are adjacent to each other to simulate the conditions of an image area and adjacent background area.

9. The system set forth in claim 8 wherein said pickup 10. The system set forth in claim 9 wherein said program circuit means applies said first potential periodically to said first area.

1 l. The system set forth in claim 10 wherein said pro- 12. The system set forth in claim 11 wherein said pro- 5 13. For use with an electrophotographic reproductoner pickup means for attracting the toner particles from the developer mix handled by the developer unit and including a pickup member separate from the latent image pattern and divided into at least first and second surface areas substantially insulated from each other,

program circuit means for applying a first electrical potential to said first area and a second electrical potential different than said first electrical potential to said second area, said first electric potential being of a polarity to attract the toner particles to said first area and corresponding to the imaged areas of the image pattern to be developed, said second electric potential corresponding to the background areas of the image pattern to be developed, a source of light, means for sensing the light reflected from said first area to provide a signal representative of the light intensity, and I control circuit means connected to said sensing means for providing a toner concentration signal representative of the effective difference between said clean and tone signals compared to a reference signal corresponding to an ideally developed image.

14. The system set forth in claim 13 wherein said control circuit means includes logarithmic amplifier means receiving said tone and clean signals and peakto-peak detector means coupled to the output of said amplifier means for providing said toner concentration signal.

15. In an electrophotographic reproduction apparatus having an insulation member for carrying a latent image pattern and a developer unit with means for applying toner to the image pattern from a mix of toner and carrier particles, a system for sensing the ability of the developer mix to supply sufficient toner for developing the image pattern at a satisfactory optical density level, said system comprising:

toner pickup means for attracting toner particles from said developer application means, said pickup means including a toner pickup member with a surface in operative engagement with said application means and independent of said insulation member for receiving said toner from said application means,

circuit means for alternately applying a toning electrical potential and a cleaning electrical potential to said pickup member surface area to attract and remove said toner, respectively,

a source of light, and

sensing means for sensing the intensity of light reflected from said pickup member area both when said toning and cleaning electrical potentials are applied providing output signals which together are representative of concentration of deposited toner.

16. The system set forth in claim 16 wherein said pickup member surface comprises first and second areas substantially insulated from each other, said circuit means applying said toning and cleaning potentials to said first area and associated toning and second potentials corresponding to the image and background areas respectively of the latent image pattern.

17. The system set forth in claim 16 wherein said first and second areas are adjacent to each other to simulate the conditions of an image area and adjacent background area.

18. The system set forth in claim 16 wherein said pickup member comprises a rotatably mounted member in operative engagement with said developer applicator means for receiving toner therefrom.

19. The system set forth in claim 18 wherein said pickup member is disposed within said developer to return toner to the mix when the pickup member is periodically cleaned.

20. The system set forth in claim 19 wherein said developer application means includes magnetic brush means.

21. For use with an electrophotographic reproduction apparatus having a developer unit for depositing toner onto a latent image pattern from a developer mix containing toner particles and carrier particles, a system for sensing the concentration of toner in the mix, said system comprising:

toner pickup means associated with the developer unit for attracting toner particles from the developer mix and including a rotatable pickup member having an outer surface area adapted to receive toner particles from the developer mix, program circuit means for successively applying tone and clean potentials to said pickup member, said tone potential causing attraction of toner onto said outer surface area and said clean potential causing repulsion of said toner from said outer surface area, a source of light irradiating said outer surface area, means for sensing the light reflected from said outer surface area with and without toner deposited thereon to provide tone and clean signals, respectively.

and control circuit means connected to said sensing means for providing a toner concentration signal representative of the effective difference between said clean and tone signals compared to a reference signal corresponding to an ideally developed image.

22. The system set forth in claim 21 wherein said control circuit means includes logarithmic amplifier means receiving said toner and clean signals and peakto-peak detector means coupled to the output of said amplifier means for providing said toner concentration signal. 

1. For use with an electrophotographic reproduction apparatus having a developer unit for depositing toner onto a latent image pattern from a developer mix containing toner particles and carrier particles, a system for sensing the effective concentration of toner in the mix, said system comprising: toner pickup means for attracting the toner paticles from the developer mix handled by the developer unit and including a rotatably mounted pickup member separate from the latent image pattern and divided into at least first and second surface areas substantially insulated from each other, means for rotating said pickup member, program circuit means for applying a first electrical potential to said first area and a second electrical potential different than said first electrical potential to said second area, said first electric potential being of a polarity to attract the toner particles to said first area and corresponding to the imaged areas of the image pattern to be developed, said second electric potential corresponding to the background areas of the image pattern to be developed, a source of light, and means for sensing the light reflected from said first area to provide a signal representative of the light intensity.
 2. The system set forth in claim 1 wherein said program circuit means applies said first potential periodically to said first area.
 3. The system set forth in claim 2 wherein said program circuit means alternately applies a cleaning potential to said first area, whereby the deposited toner particles are periodically removed.
 4. The system set forth in claim 3 wherein said cleaning potential is equal to said second potential.
 5. The system set forth in claim 4 wherein said program circuit means alternately applies said first and second potentials to said second area.
 6. The system set forth in claim 5 wherein said first and second areas are adjacent to each other to simulate the conditions of an image area and adjacent background area.
 7. For use with an electrophotographic reproduction apparatus having a developer unit for depositing toner onto a latent image pattern from a developer mix containing toner particles and carrier particles, a system for sensing the effective concentration of toner in the mix, said system comprising: toner pickup means for attracting the toner particles from the developer mix handled by the developer unit and including a pickup member separate from the latent image pattern and divided into at least first and second surface areas substantially insulated from each other, program circuit means for applying a first electrical potential to said first aRea and a second electrical potential different than said first electrical potential to said second area, said first electric potential being of a polarity to attract the toner particles to said first area and corresponding to the imaged areas of the image pattern to be developed, said second electric potential corresponding to the background areas of the image pattern to be developed, a source of light, and means for sensing the light reflected from said area to provide a signal representative of the light intensity, said pickup member comprising a rotatably mounted member associated with the developer unit, said first and second areas being axially disposed of each other.
 8. The system set forth in claim 7 wherein said first and second areas are adjacent to each other to simulate the conditions of an image area and adjacent background area.
 9. The system set forth in claim 8 wherein said pickup member includes a third surface area electrically insulated from and axially adjacent to said first surface area, said first surface area being disposed intermediate said second and third surface areas, said program circuit means applying said second electrical potential corresponding to the background of the image pattern to said third toning area.
 10. The system set forth in claim 9 wherein said program circuit means applies said first potential periodically to said first area.
 11. The system set forth in claim 10 wherein said program circuit means alternately applies a cleaning potential to said first area, whereby the deposited toner particles are removed periodically.
 12. The system set forth in claim 11 wherein said program circuit means alternately applies said first and second potentials to said second area and to said third area.
 13. For use with an electrophotographic reproduction apparatus having a developer unit for depositing toner onto a latent image pattern from a developer mix containing toner particles and carrier particles, a system for sensing the effective concentration of toner in the mix, said system comprising: toner pickup means for attracting the toner particles from the developer mix handled by the developer unit and including a pickup member separate from the latent image pattern and divided into at least first and second surface areas substantially insulated from each other, program circuit means for applying a first electrical potential to said first area and a second electrical potential different than said first electrical potential to said second area, said first electric potential being of a polarity to attract the toner particles to said first area and corresponding to the imaged areas of the image pattern to be developed, said second electric potential corresponding to the background areas of the image pattern to be developed, a source of light, means for sensing the light reflected from said first area to provide a signal representative of the light intensity, and control circuit means connected to said sensing means for providing a toner concentration signal representative of the effective difference between said clean and tone signals compared to a reference signal corresponding to an ideally developed image.
 14. The system set forth in claim 13 wherein said control circuit means includes logarithmic amplifier means receiving said tone and clean signals and peak-to-peak detector means coupled to the output of said amplifier means for providing said toner concentration signal.
 15. In an electrophotographic reproduction apparatus having an insulation member for carrying a latent image pattern and a developer unit with means for applying toner to the image pattern from a mix of toner and carrier particles, a system for sensing the ability of the developer mix to supply sufficient toner for developing the image pattern at a satisfactory optical density level, said system comprising: toner pickup means for attracting toner particles from said developer application means, said pickup means Including a toner pickup member with a surface in operative engagement with said application means and independent of said insulation member for receiving said toner from said application means, circuit means for alternately applying a toning electrical potential and a cleaning electrical potential to said pickup member surface area to attract and remove said toner, respectively, a source of light, and sensing means for sensing the intensity of light reflected from said pickup member area both when said toning and cleaning electrical potentials are applied providing output signals which together are representative of concentration of deposited toner.
 16. The system set forth in claim 16 wherein said pickup member surface comprises first and second areas substantially insulated from each other, said circuit means applying said toning and cleaning potentials to said first area and associated toning and second potentials corresponding to the image and background areas respectively of the latent image pattern.
 17. The system set forth in claim 16 wherein said first and second areas are adjacent to each other to simulate the conditions of an image area and adjacent background area.
 18. The system set forth in claim 16 wherein said pickup member comprises a rotatably mounted member in operative engagement with said developer applicator means for receiving toner therefrom.
 19. The system set forth in claim 18 wherein said pickup member is disposed within said developer to return toner to the mix when the pickup member is periodically cleaned.
 20. The system set forth in claim 19 wherein said developer application means includes magnetic brush means.
 21. For use with an electrophotographic reproduction apparatus having a developer unit for depositing toner onto a latent image pattern from a developer mix containing toner particles and carrier particles, a system for sensing the concentration of toner in the mix, said system comprising: toner pickup means associated with the developer unit for attracting toner particles from the developer mix and including a rotatable pickup member having an outer surface area adapted to receive toner particles from the developer mix, program circuit means for successively applying tone and clean potentials to said pickup member, said tone potential causing attraction of toner onto said outer surface area and said clean potential causing repulsion of said toner from said outer surface area, a source of light irradiating said outer surface area, means for sensing the light reflected from said outer surface area with and without toner deposited thereon to provide tone and clean signals, respectively, and control circuit means connected to said sensing means for providing a toner concentration signal representative of the effective difference between said clean and tone signals compared to a reference signal corresponding to an ideally developed image.
 22. The system set forth in claim 21 wherein said control circuit means includes logarithmic amplifier means receiving said toner and clean signals and peak-to-peak detector means coupled to the output of said amplifier means for providing said toner concentration signal. 